Add more [[nodiscard]] attributes

Automatically detected using clang-tidy with modernize-use-nodiscard check.

src/DynamicModel.hh

@@ -73,7 +73,8 @@ public:
     void checkAllRegimesPresent() const noexcept(false);
 
   private:
-    pair<vector<string>, vector<string>> convertBitVectorToRegimes(const vector<bool>& r) const;
+    [[nodiscard]] pair<vector<string>, vector<string>>
+    convertBitVectorToRegimes(const vector<bool>& r) const;
   };
 
 private:

src/HeterogeneityTable.hh

@@ -90,7 +90,7 @@ public:
   };
 
   void addSummedHeterogeneousEndogenous(int symb_id);
-  int getSummedHeterogenousEndogenousIndex(int symb_id) const;
+  [[nodiscard]] int getSummedHeterogenousEndogenousIndex(int symb_id) const;
   [[nodiscard]] int aggregateEndoSize() const;
 
   void writeOutput(ostream& output) const;